Concerned about black little dots in bones

[u/mossy_queerdo]

I tried finding similar posts or good answers in this sub before, but couldn't find anything helpful for my case... So there are these little black spots in many of the weasel bones I have, even after whitening with hydrogen peroxide (3 %, nearly 24 hours). They are very visible if the bones are wet, but you can also find them if everything is completely dry. Are they something I should be worried about for the future? Is it mold, is it trapped dirt? Was my degreasing process not complete and it's simply fat that just looks suspicious? I hope you can give me some answers because it's driving me insane...